1. Field of the Invention
The invention relates to amplitude modulation envelope detectors having a wide operating range and which are provided with temperature drift compensation.
2. Description of the Prior Art
Amplitude modulation envelope detectors have been employed in radar and other systems to obtain video bandwidth information frequencies as a linear function of the modulated carrier signal. Since, in these systems, the modulation bandwidth may be on the order of Mega-Hertz or considerably greater, in order to obtain the modulation frequencies at the output of the detector in a linear manner, the impedance acting as a load is generally maintained small to provide a wide video bandwidth. However, for small load impedances, low amplitude input signals to the detector become affected by the non-linear region of the operating characteristics of the detector components. Increasing the envelope detector drive level to remain above the component non-linear operating region had the disadvantage of requiring high drive power requirements for the detector. Therefore, forward biasing of the detector components has been employed to improve the linearity of component operating characteristics at low input levels. However, the temperature drift component characteristics of these forward biased detectors resulted in an unstable offset voltage causing the loss of low level input signals. Without temperature compensation, a stable offset voltage could not be maintained over a range of ambient temperatures.
The invention herein described was made in the course of or under a contract or subcontract thereunder with the Department of the Air Force.